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Microfluidics is a flourishing field, enabling a wide range of biochemical and clinical applications such as cancer screening, micro-physiological system engineering, high-throughput drug testing, and point-of-care diagnostics. However, fabrication of microfluidic devices is often complicated, time consuming, and requires expensive equipment and sophisticated cleanroom facilities. Three-dimensional (3D) printing presents a promising alternative to traditional techniques such as lithography and PDMS-glass bonding, not only by enabling rapid design iterations in the development stage, but also by reducing the costs associated with institutional infrastructure, equipment installation, maintenance, and physical space. With the recent advancements in 3D printing technologies, highly complex microfluidic devices can be fabricated via single-step, rapid, and cost-effective protocols, making microfluidics more accessible to users. In this review, we discuss a broad range of approaches for the application of 3D printing technology to fabrication of micro-scale lab-on-a-chip devices.

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Despite the extensive commercial use of Li 1-x Ni 1-y-z Mn z Co y O 2 (NMC) as the positive electrode in Li-ion batteries, and its long research history, its fundamental transport properties are poorly understood. These properties are crucial for designing high energy density and high power Li-ion batteries. Here, the transport properties of NMC 333 and NMC 523 are investigated using impedance spectroscopy and DC polarization and depolarization techniques. The electronic conductivity is found to increase with decreasing Li-content (increasing state-of-charge) from ∼10 −7 Scm −1 to ∼10 −2 Scm −1 over Li concentrations x = 0.00 to 0.75, corresponding to an upper charge voltage of 4.8 V with respect to Li/Li + . The lithium ion diffusivity is at least one order of magnitude lower, and decreases with increasing x to at x = ∼0.5. The ionic conductivity and diffusivity obtained from the two measurements techniques (EIS and DC) Cathodes having high energy and power density, adequate safety, excellent cycle life, and low cost are a critical need for Li-ion batteries to enable the commercialization of electric transportation and stationary storage.1 Towards this end, much previous research focused on the development of LiNi 1-x Co x O 2 (NC) 2-10 cathode due to its high capacity (∼275 mAh/g) and favorable operating cell voltage (4.3 V vs. Li/Li + ), which is within the voltage stability window of current liquid electrolytes, and lower cost than LiCoO 2 . Despite extensive optimization, e.g., with respect to the Ni/Co ratio, 2-10 NC suffers from poor structural stability during electrochemical cycling. 11Significant efforts were subsequently focused on improving structural stability and electrochemical performance by partial substitution Mn 12-17 (electrochemically inactive in this compound over the operating cell voltage window). Thus our objective in this work is to systematically characterize and interpret the transport properties of NMC 333 and NMC 523 . We use additive-free, single phase sintered samples in which the extrinsic effects due to binders, conductive additives, and particle microstructures that may be present in composite electrodes are avoided. Using electron blocking and ionic blocking cell configurations, respectively, and electrochemical impedance spectroscopy and DC polarization and depolarization techniques (see Table I), we deconvolute the electronic and ionic conductivities of NMC 333 and NMC 523 as a function of temperature and Li content, up to a lithium deficiency of x = 0.75, which corresponds to high charge voltages of 4.7 V and 4.8 V for NMC 333 and NMC 523 respectively. Our sample configuration permits measurement of single-phase properties up to delithiation levels (state-of-charge) where electrochemically-induced microfracture intrudes. Electronic conductivity was not apparently affected by these effects, whereas ionic transport shows an apparent increase beyond x = 0.50 which we attribute to fast transport paths created by microfracture. • C for 12 h in ambient atmosphere, preceded by h...

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The prevailing electrode fabrication method for lithium-ion battery electrodes includes calendering at high pressures to densify the electrode and promote adhesion to the metal current collector. However, this process increases the tortuosity of the pore network in the primary transport direction and imposes severe tradeoffs between electrode thickness and rate capability. With the aim of understanding the impact of pore tortuosity on electrode kinetics, and enabling cell designs with thicker electrodes and improved cost and energy density, we use here freeze-casting, a shaping technique able to produce low-tortuosity structures using ice crystals as a pore-forming agent, to fabricate LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes with controlled, aligned porosity. Electrode tortuosity is characterized using two complementary methods, X-ray tomography combined with thermal diffusion simulations, and electrochemical transport measurements. The results allow comparison across a wide range of microstructures, and highlight the large impact of a relatively small numerical change in tortuosity on electrode kinetics. Under galvanostatic discharge, optimized microstructures show a three-to fourfold increase in area-specific capacity compared to typical Li-ion composite electrodes. Hybrid pulse power characterization (HPPC) demonstrates improved power capability, while dynamic stress tests (DST) shows that an area-specific area capacity corresponding to 91% of the NCA galvanostatic C/10 capacity could be reached. With the ever-increasing demand for mobile applications and the growing concern for the replacement of fossil fuels, alternative energy storage has become an increasingly pressing but still unsolved problem.1-3 Because of their unequalled combination of high energy and power density, lightweight design and excellent lifespan, lithiumion batteries are to date the technology of choice for portable electrochemical storage, powering applications such as electronic devices, power tools and hybrid/full electric vehicles. The prevailing electrode fabrication method for lithium-ion battery electrodes includes high pressure calendering of electrode formulations that include active lithium materials, organic binder and conductive additives, in order to densify the electrode and promote adhesion to the metal current collector. However, this process also increases the tortuosity of the pore network in the primary transport direction. In practice, to meet operational C-rates desired, and production throughput objectives, the thicknesses of commercial electrodes are restricted to less than ∼100 μm. Beyond this value, ion transport becomes a limiting factor and the accessible specific capacity starts to drop dramatically. 4 With the aim of increasing cell energy density and decreasing cost by building thicker electrodes, several strategies to reduce pore tortuosity by aligning the porosity in the direction normal to the current collector have been proposed. Bae et al.5 demonstrated through modeling and experiments that a dual-sc...

The electronic conductivity of lithium titanate spinel (Li4/3Ti5/3O4) is measured as a function of lithiation and temperature. The electronic conductivity of fully lithiated spinel (Li7/3Ti5/3O4) is 2.46 S cm−1 at 300 K and is weakly thermally activated. High electronic conductivity is observed over a wide lithiation range down to x~0.04 and suggests that lithium chemical diffusion is ionically limited over most of the state of charge regime.

Based on experimental results, in particular, obtained on single crystals, the nature of the decisive point defects and charge carriers in LiFePO 4 is discussed, and the dependencies of their concentrations on the control parameters Li activity, doping content, and temperature are worked out. In the native regime characterized by Li deficiency ␦, lithium vacancies being decisive for ion conduction are compensated by holes as decisive electronic carriers. Very close to the concentration of order ͑where ␦ is strictly zero͒ frozen-in native defects or non-intentional impurities dominate. We typically found lithium vacancies compensated by iron atoms on Li sites ͑Fe Li ͒. Intentionally introduced donors such as Al Fe or Si Fe , have the same donor effect. The Brouwer diagrams displaying the logarithm of the defect concentration vs log lithium activity or vs log donor/acceptor content are derived. As to the temperature dependence of conductivities, trapping of holes by lithium vacancies is crucial and dominates the effective activation barrier at frozen lithium content. In particular, for the Al-doped samples, ionic association also proves important. Defect reaction and migration enthalpies are derived for electronic and ionic transport. Trapping of holes by lithium vacancies and association of lithium vacancies with impurities also turn out to be key for understanding the temperature dependence of the chemical diffusion coefficient of lithium.